1. Field of the Invention
This invention relates to adhesive cementing agents for the hard tissues of the human body, including teeth and bones. More particularly, the invention relates to adhesive cementing agents of the type in which an intimate bonding affinity for human tissues is desired, such as cements for the treatment of a complex fracture of bone or for fixation of artificial joints, dental adhesives, dental fillers, dental restorative, and so forth.
2. Description of the Prior Art
In the conventional dental filling agents of the coldcure type (curable at room temperature) as well as the cementing agents for the fixation of artificial joints, a mixture of polymethyl methacrylate and methyl methacrylate or a mixture of bisphenol-A diglycidyl dimethacrylate and triethylene glycol dimethacrylate, among other combinations, are employed and allowed to cure in situ in the presence or absence of an inorganic filler, mainly by means of a peroxide-amine catalyst system which generates free radicals. The cured composition obtainable by this known method has substantially no bonding affinity for human tissues (except for acid treated dental enamel), the bonding strength under wet conditions being as low as about 0 to 5 kg/cm.sup.2. For this reason, in the conventional filling practice, e.g. for the treatment of caries, mechanical retainer means known as undercuts have been applied to the cavity to lock the cured filling agent in position. This procedure, however, is disadvantageous in that it removes the healthy portion of the tooth and in that because of the lack of bond between the filler and the tooth proper, it provides only a poor marginal seal which often permits a relapse of tooth decay or other tissue defect. As a preventive filling agent and an orthodontial cement, both adapted to provide a sealing bond with the tooth, adhesive agents based on .alpha.-cyanoacrylate have been developed in recent years, but these agents are known to lack durability in the oral cavity as well as have poor handleability. A dental cement-filling agent containing a trialkylboron compound as a polymerization initiator ingredient has also been developed (Japanese Patent Publication No. 14318/1967 and No. 29195/1970), but while it provides a firm bond with the dentin, it does not have adequate bonding affinity for the enamel. Moreover, since the resin employed is primarily based on methyl methacrylate, this product is not fully satisfactory for dental filling purposes. A procedure has also been developed which employs a vinyl compound containing a divalent phosphoric acid ##STR2## group which is claimed to provide a bond with the calcium of the tooth (Japanese Patent Application laid-open No. 44152/1976; Journal of Dental Research 35, 846). However, its low adhesive strength does not make the product sufficiently useful for most practical purposes. U.S. Pat. No. 3,882,600 discloses that the addition of a small amount of an addition-polymerizable phosphoryl monofluoride to a dental cement composition results in an improved bond between the tooth and the composition. However, this product seems to be not truly safe to the pulp because of its interaction with the tooth which is conceivably due to the P-F bond contained in the product.